ABB Motor Signature Analisis

Sr. No.6638AA01 Rain CII Carbon Ltd, Vizag

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AANNAALLYYSSIISS

PPRROOGGRRAAMM

Customer Rain CII Carbon Ltd – Vizag.

Machine BFP Motor – A, Motor M4

LEAP Level Standard

Date of Testing 18-09-2011

Date of report dispatch 29-11-2011

Tested By Mr. Mayur Kalesakar

Mr. N.P. Sali

Report Prepared By

Ameet Choughule

Report Approved By Cajetan Pinto

L . E

. A

. P

.


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MACHINE DETAILS

Serial No 6638AA01

Make Westinghouse Motor Company - Texas

Year 1997

Rated Output 1250 HP

Stator Volts 6600 V

Stator Current 93 A

Class of Insulation F

Connection Y

Rated Frequency 50

Speed (RPM) 2963

Machine condition at time of testing:

Machine Assembled: Yes Winding Temperature: 40 deg. PDCA Test Voltage: 2500 V Maximum AC Test Voltage: 3800.0 V

Assumptions/Information on stator winding design and construction:

Stator has Class F epoxy mica based insulation system. Stress grading system is considered at the slot ends. Corona protection shield is used in slot regions.


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SUMMARY

The following is the analysis for the stator winding insulation:

There is evidence of presence of abnormal charge accumulation post overhauling on the stator

windings.

Volume resistivity values obtained are found to be low because of presence of moisture in the

leads/termination areas of the winding. This is also the reason for having low PI values.

There is evidence of erosion/damage in the corona protection shield used in slot region.

There is evidence of damage/modification to the stress grading system used at slot ends.

There is evidence of the presence of mobile ions in the insulation system. From the extent of de-

polymerization of the resin, the state of ageing of the resin can be described as "mid-life”.

Discharging in internal de-laminations is one of the modes of discharge activity. The extent of

discharging air spaces, measured by the discharging void volume content, is greater than what is

normally observed in epoxy-mica insulation systems.

On the basis of the operating data and the measurements performed on the machine and based on

the lifetime expectancy analysis and the condition of the machine insulation, the machine has been in

operation for a period of around 55.64% of the expected lifetime of the stator winding. The expected

life of the stator winding insulation is estimated to be an additional 47200 equivalent operating

hours with the existing operating conditions. The above life expectancy analysis is done with a

confidence level of 80%.


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RECOMMENDATIONS

The unit has been cleaned along the overhang and significant improvement is observed in IR and PI values after partial cleaning done. However LEAP Standard test carried on the machine indicate that there is still presence of significant charge accumulation on the winding surface mainly due to presence of oil and moisture contamination along with the slot discharging activity.

A Level 4 maintenance intervention is recommended to be performed at the earliest or time period not exceeding 3 months of operation. This outage requires removal of rotor:

The following maybe done in the intervention: Cleaning and Dry-out of Stator Windings:

The windings have to be overhauled using dry ice cryogenic cleaning or solvent cleaning and subsequently heated using hot air blowers at temperatures around 80 – 85 deg C, to dispel surface moisture/solvent residues before starting up the machine. Areas along the end-winding such as near the tie-ups or any visible cracks, should be observed for oozing of oil during the heating process. This cleaning and heating process may be repeated in cyclic fashion for 2 to 3 times, till there is no more oil oozing. Unit may be varnished subsequently and dried out again to cure the surface varnish. This will seal any surface cracks or pores and prevent any further ingress.

Cleaning and Dry-out in the region of the Stator Winding Terminations and leads The termination areas of the windings have to be cleaned and heated to remove suspected causes of localized high insulation leakage.

Inspection of the slot and slot end areas The un-wedged portions of the slot areas should be inspected for any signs of damage. In cases where the wedges cover the entire slot length, areas of the coil sides that are accessible at the slot ends or through vent duct spaces should be visually inspected. In case magnetic slot wedges are used they should be checked for any wear/damage. The areas around the stator end-windings should be inspected. The inspection could be aided with appropriate endoscopes. Alternatively, the inspection could be aided with a corona detection probe for localization of the discharge activity, when the windings are energized.

Other Inspections: In addition to providing a maintenance opportunity for the recommended maintenance actions, the inspection helps cover the portions of the winding that cannot be evaluated in a LEAP Standard inspection e.g. end-winding support system, specific localized damage areas, wedge tightness, etc .


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Further assessment:

It is advised to perform a LEAP Standard inspection after the above actions to monitor for improvements in

the discharge related damage

the extent of de-lamination

the extent of resin de-polymerization

the increase in suspected winding contamination

and to re-evaluate the need and schedule for further maintenance.


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COMMENTS The details of measurements and analyzed parameters with the glossary can be found in the Appendix.

CONTAMINATION:

There is evidence of presence of abnormal charge accumulation post overhauling due to the following reasons:

Charge magnitudes Q1, Q2 and Q3 are charges corresponding to various physical phenomena in slot, slot-end and end-winding regions respectively. The general charge storage as determined from the PDCA for all the three phases simultaneously tested is found to be higher than the normally observed values for windings without contamination.

Also due to internal star connection, test could only be done on UVW combined phase where effectively only the slot section is tested. Hence, end-windings where the contamination is usually higher could have yielded even higher charge storage values, if individual phases were tested with respect to ground.

The dispersion ratio correspondingly is also on higher side. The readings have been taken post overhauling and thus evidently the contaminants have been

removed. However there is still presence of significant charge accumulation on the winding surface mainly due to presence of oil and moisture contamination. The distributed nature of charge storage suggests moisture condensation within the motor post overhauling, during testing.

The Ic/Ir value obtained when all three phases are simultaneously tested is indicative of the nature of the dominant current that flows on the surface of the end-windings at the slot ends.

Negative Ic/Ir values are indicative of the flow of currents being controlled by electrochemical charge storage effects, or by presence of homopolar charges. Homopolar charges can be created either by the presence of moisture in the contaminant or due to excessive humidity. In the present case it may be due to the presence of moisture in the contaminants.

The volume resistivity is below the normal range for the class of insulation used. This is most likely due to the presence of homopolar charges and the possibility of presence of moisture in the leads/termination areas of the winding, which could lead to increased leakage currents during charging measurements. This is also the reason for having low PI values.

CONDITION OF CORONA PROTECTION SHIELD: There is evidence of damage or erosion to the corona protection shield used in the winding from to the following:

The partial discharge patterns obtained are indicative of slot discharge activity which means that there could be some degradation of the corona protection shield. Also the void content as calculated from tan delta and capacitance variations with voltage, when all three phases are tested together, is higher than what is normally observed in epoxy mica insulation systems and could have significant contributions from discharging in air spaces between the coil and the slot. This needs to be monitored.

There is some evidence of lack of electrical contact of the corona protection shield with the stator core. This could be possible due to looseness or due to damage/modification of the corona protection shield or due to the presence of an insulating layer between the corona protection shield and the slot.


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CONDITION OF THE STRESS GRADE SYSTEM :

There is evidence of damage/modification to the properties of the stress grading system at the slot ends due to the following reasons:

The partial discharge patterns consist of a distinctive number of sharp pulses of equally high magnitude that are clustered randomly in the voltage cycle. These discharges are characteristic of PD at slot exits and are likely due to developing modification/damage of the stress grading system used at the slot ends. This needs to be monitored.

The variation of tan delta and capacitance with voltage below discharge inception, is seen to be linear in nature. This behavior is essentially governed by the surface properties of the windings at the slot ends.

AGEING OF THE RESIN: There are indications of the presence of mobile ions in the insulation from the following: The harmonic patterns obtained on analyzing the instantaneous admittance of the insulation is

representative of the predominance of non-linear effects due to an accumulation of mobile ions within the insulation system. This is mainly due to presence of surface contaminants and moisture present in winding and not due to ageing.

The extent of accumulation of mobile ions, which is attributed to the process of resin de-polymerization, is in accordance with what is expected from the operating parameters of the stator winding.

From the extent of de-polymerization of the resin, the state of ageing of the resin can be described as “mid-life”.

DELAMINATION: There is evidence of excessive discharging in de-lamination/voids within the insulation as can be seen from the following:

From the discharge patterns it is evident that discharging in internal voids/de-laminations is the most dominant discharge activity and the voids/de-laminations are seen to be distributed through the volume of the insulation.

The discharging void volume content calculated from tan delta and capacitance variations with voltage when all three phases are simultaneously tested, and estimated at the line to ground test voltage, is on the higher side (> 0.5%) when compared with similar epoxy mica based insulation systems. This needs to be monitored.


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STATOR WINDING RESISTANCE @ 40 0C

PHASE U – V V – W W – U

RESISTANCE (mΩ) 816.8 816.4 817.3

The unbalance is only 0.06 % as against the permissible limit of < 3 %.

POLARISATION-DEPOLARISATION CURRENT ANALYSIS (PDCA) (Before Overhauling)

Test Voltage: 2500 V dc Stator:

UVW

NORMAL RANGE

IR (INSULATION RESISTANCE) [M] 647 -----

PI (POLARIZATION INDEX) 1.19 >2

T1 (ION MIGRATION TIME CONSTANT) [secs] 19.72 10 – 30

Sec

T2 (SLOW RELAXATION TIME CONSTANT) [secs] 109.73 65 – 150

Sec

T3 (INTERFACIAL POLARIZATION TIME CONSTANT) [secs] 697.29 300 – 1000

Sec

Q1 (CHARGE - ION MIGRATION) [%] 21.86 < 7%

Q2 (CHARGE - SLOW RELAXATION) [%] 16.99 < 10%

Q3 (CHARGE - INTERFACIAL POLARIZATION) [%] 19.94 < 20%

Q1/Q2 128.65 55-65

Q2/Q3 85.22 55-65

AGEING FACTOR 42.18 35-100

Ic/Ir -0.49 -----

Co/C (DISPERSION RATIO) 1.59 < 1.25

I (CHARGING CURRENT AT LONG TIMES) [A] 3.2547 -----

VOLUME RESISTIVITY (Log Scale) 12.261 > 14


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POLARISATION-DEPOLARISATION CURRENT ANALYSIS (PDCA) (After Overhauling)

Test Voltage: 2500 V dc Stator:

UVW

NORMAL RANGE

IR (INSULATION RESISTANCE) [M] 5089 -----

PI (POLARIZATION INDEX) 3.01 >2

T1 (ION MIGRATION TIME CONSTANT) [secs] 20.19 10 – 30

Sec

T2 (SLOW RELAXATION TIME CONSTANT) [secs] 121.33 65 – 150

Sec

T3 (INTERFACIAL POLARIZATION TIME CONSTANT) [secs] 766.06 300 – 1000

Sec

Q1 (CHARGE - ION MIGRATION) [%] 10.51 < 7%

Q2 (CHARGE - SLOW RELAXATION) [%] 14.96 < 10%

Q3 (CHARGE - INTERFACIAL POLARIZATION) [%] 25.29 < 20%

Q1/Q2 70.29 55-65

Q2/Q3 59.15 55-65

AGEING FACTOR 62.26 35-100

Ic/Ir -2.94 -----

Co/C (DISPERSION RATIO) 1.51 < 1.25

I (CHARGING CURRENT AT LONG TIMES) [A] 0.1126 -----

VOLUME RESISTIVITY (Log Scale) 13.722 > 14


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TAN DELTA & CAPACITANCE MEASUREMENTS

Voltage (kV)

UVW

TD (%) CAP (pF)

0.5 13.608 59030

1.0 14.036 59220

1.5 14.548 59710

2.0 14.895 59840

2.5 15.031 59990

3.0 15.395 59960

3.5 15.683 60200

3.8 16.115 60170

Calculated parameters:

UVW

Effective Phase Shift (deg) 49.60

Base Tan Delta TDo (%) 13.35

Base Capacitance Co (pF) 58916

Discharge Inception Voltage (kV) 3.00

Discharging Void Volume Content (%) 1.22

Effective Phase of Discharge (deg) -4.33

58800

59050

59300

59550

59800

60050

60300

60550

0

3

6

9

12

15

18

21

0 0.5 1 1.5 2 2.5 3 3.5 4

Ca

pa

cit

an

ce (p

F)

Ta

n D

elt

a (%

)

Voltage (kV)

TAN DELTA & CAPACITANCE MEASUREMENTS

Tan Delta Capacitance

Tan Delta -CAP

0.01

0.1

1

10

1 10 100 1000

Po

l-D

ep

ol C

urr

en

ts (

mic

roA

mp

)

Time (sec)

Polarization-Depolarization CurrentsUVW Phase

Charging Discharging PDCA


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NON-LINEAR INSULATION BEHAVIOUR ANALYSIS (NLIBA)

0.000

2.000

4.000

6.000

8.000

10.000

12.000

14.000

1 3 5 7 9 11 13 15

OD

D H

AR

MO

NIC

MA

GN

ITU

DE

(a

rbit

rary

un

its

)

ODD HARMONICS

1

2

3

3.8

0.000

5.000

10.000

15.000

20.000

25.000

2 4 6 8 10 12 14 16

EV

EN

HA

RM

ON

IC M

AG

NIT

UD

ES

(a

rbit

rary

un

its

)

EVEN HARMONICS

1

2

3

3.8


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PARTIAL DISCHARGE ANALYSIS (PDA)

<Phase UVW @ 2.99 kV> <Phase UVW @ 3.77 kV>


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LIFE EXPECTANCY ANALYSIS A combined stress phenomenological model, that is based on one proposed originally by Simoni, Srinivas, et al, is used to assess the extent of degradation of the insulation and perform a lifetime expectancy analysis. The model accounts for thermal, electrical and mechanical stresses, whose relative effects on the life of the insulation are estimated on the basis of the analysis from the measurements performed, and from the operating and historical details made available. The theory stems from the fact that when stresses act on the insulation of the stator windings, there is a progressive deterioration of the strength of the insulation. In other words, ageing is exhibited by a progressive deterioration of the physical properties of the insulation. Not all physical properties can give an indication of the progression of ageing, except perhaps those directly related to failure, e.g. electrical breakdown strength and mechanical strength. If stresses unable to produce a failure are considered such as temperature or chemical exposure, other failure criteria are selected that are related to electrical or mechanical breakdown strengths. In any case, failure essentially occurs when the selected property drops down to a limiting value, so that a unique definition can be adopted for remaining life – the time for the selected property to reach that point. This point is generally related to the stresses that are developed in the stator insulation during machine operation. In other words, when the strength of the insulation deteriorates to a point where it equals the developed stresses in the insulation, the insulation will fail. The measurements performed during an inspection are converted into parameters that can be related to the stresses that are developed in the insulation, for example the extent to air space within insulation would affect thermal, mechanical and electrical properties of the insulation and thereby affect the thermal electrical and mechanical stresses that are developed in the insulation. This affects the rate of deterioration of the insulation. To give another example, when the temperature of the insulation increases, the rate of deterioration of the mechanical strength of the insulation also increases. Therefore, based on the knowledge of how parameters derived from measurements can affect stresses, it is possible to estimate the rate of deterioration of the strength of the insulation. In the case of LEAP Standard measurements performed, the parameters that have been used as inputs from the analysis include the charge distribution parameters, the volume resistivity, the discharging void content parameters, partial discharge parameters and data from the non-linear analysis. These parameters are used together with operating data such as winding temperature and the number of starts, to draw the line describing the deterioration in insulation strength, as indicated by the dashed red line. It is generally assumed that at the time of commissioning of the machine, there is no deterioration of the relevant properties of the insulation. An initial life estimate, indicated by the solid red line up to the time of inspection and projected by the dashed green line, is made on the basis of “normal” expected parameters (as derived from operating data and the normal range values of measurements such as those specified for LEAP Standard inspections) at an early part of the machine life. Operational hours: 43200 (data provided)

Starts/stops: 800 (data provided)

Equivalent hours: 59200 (Op. Hours + 20 * Starts/Stops)

Maximum Winding Temperature: 85.0 Deg C (data provided)

Life Consumed: 55.64%


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0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

% L

Ife

Us

ed

Up

Equivalent Hours ( x 1000)

LIFE EXPECTANCY ANALYSIS @ 85 deg C (With 80 % Confidence Level)

Insulation degradation curve (designed) Remaining Life (present) Present Life

Designed LifeEstimatePresent Life

Estimate

On the basis of the operating data and the measurements performed on the stator, the expected life of the stator winding insulation is estimated to be an additional 47200 equivalent operating hours with the existing operating conditions. The above life expectancy analysis is done with a confidence level of 80% and considers some points as under:

a) The above estimation is based on the measurements performed by ABB and historical and operating data of the machine, made available to ABB, considering steady state conditions only.

b) The life estimation is based on the assessment of the stator ground-wall insulation only. Models are used that describe known wearing out and ageing processes of the ground-wall insulation of the stator windings.

c) It is assumed in the analysis, that future operating conditions of the machine will be similar to the historical operating data made available to ABB.

d) Any transient stresses that may be manifested on the windings, such as switching and/ external line transients, etc., could result in insulation failure prior to estimated life (pre-mature failure).

e) The aim of life estimation study is aimed at developing a maintenance plan for the stator winding. ABB disclaims warranty of merchantability or fitness for intended purpose.

f) LEAP is a process and not a one time event. Re-evaluation of measurements over a period of time will help reduce the effect of the assumptions made and could increase the confidence level of the analysis.


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GLOSSARY

Charge storage: The charge storage takes place due to various mechanisms such as,

Space charge polarization: The alignment of electric dipoles within the insulation on application of electric field results in accumulation of charges in a region such as near the electrodes (copper and iron) in the slots and in the end winding sections, due to the inefficient exchange of charges in these areas. This is called space charge polarization.

Interfacial polarization: The migration and accumulation of charge between two different dielectrics that have different dielectric constants (such as that between layers of mica-epoxy, between machine insulation and contaminant, between machine insulation and airspace, etc) gives rise to interfacial polarization. The Q2 charges usually reflect charge accumulation at interfaces within slot section, while Q3 charges usually reflect charge accumulation on the end-winding, on the basis of a distributed capacitor-resistor model that is used to describe surface conditions on the end-winding.

The proportional distribution of these charges (as seen from values of Q1/Q2 and Q2/Q3) gives an indication of the charge storage process that may be dominant. A greater proportion of charge stored near the electrodes could possibly indicate (high Q1/Q2, for thermosetting systems), a loss of electrical contact of the outer surface of the coil with the core. This may be due to high coil side clearances/ wedge looseness or damage/ degradation/ modification of the properties/erosion of the slot discharge prevention shield or even an insulating layer between the corona protection and the slot. It could also indicate possible overheating of the coil surface in contact with the core, or aging/overheating of the insulation in close proximity of the conductor stack, large gaps between the groundwall insulation and the conductor stack. Ic/Ir Ratio: Ic/Ir ratios are calculated by considering the current in the range of 1000 sec expressed as a power law curve, and essentially is representative of the flow of capacitive and resistive currents on the end-winding surface. The model used, most closely represents the situation when all three phases are simultaneously tested. The analysis is meaningful only when the presence of contaminants is indicated from other analysis such as charge storage. The ratio is meant to be indicative of the nature of the contaminant at the slot ends. Values near 1 and less than 1 have been observed in windings contaminated by carbon particles/carbonized oil (conductive contaminants) or other conductive dust deposition at the slot ends. In case of oil/grease type contaminants, discontinuity in the stress grading system at the slot ends, the values are greater than 1. Negative values are at times observed due to the creation of homopolar charges at the slot end regions, due to the present of moisture in the contaminant or on the surface of the windings or even when there is iron oxide in the contaminant.

Aging Factor (AF): This factor gives an indication of the state of resin in close vicinity of the electrodes, in terms of the concentration and mobility of its mobile ions. The values are around 100 for new machines. However, when reduced values are obtained it indicates de-polymerization of resin and aging of insulation near the electrodes. Extremely low values of AF (<35) could also be obtained if the windings are contaminated with dirt and the contaminant penetrates into the insulation, in and around electrode regions.

Ion Concentration index (CI): There are always mobile ions found within the insulation, but these are generally dispersed within the insulation. During a polarization process these charges get trapped in

Space charge polarization (Q1) and Interfacial polarization (Q2) In SLOT region

Interfacial polarization (Q3) in ENDWINDING region


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certain regions of the winding insulation. The number of mobile ions per unit volume is represented by the Ion Concentration Index. The greater the ion concentration, the higher is the possibility of charge injection within the insulation. The ion concentration index is generally reflective of the charge concentrations near the electrodes, or at interfaces. The permissible values lie between 0.015 to 0.025.

Dispersion ratio: The ratio of the capacitance required to store the charge obtained from the winding during the discharging process, to the geometrical capacitance of the windings, is referred to as the Dispersion ratio. Values computed for clean and dry insulation normally do not exceed 1.2. Dispersion ratio values have been seen to exceed 1.2,

a) if there is a dispersive contaminant present in or on the windings, e.g. carbon, particularly when mixed with oil, or moisture present in the contaminant or in the windings,

b) if there is a loss of contact of the outer surface of the coil with the core, and the presence of an insulation between the anti corona shield and core (as is sometimes seen in VPI windings),

c) in cases of advanced aging of the insulation.

Tan delta: Tan is a measure of the energy spent in the dielectric medium as a result of dipolar polarization, interfacial polarization, space charge polarization and partial discharge effects. Tan delta variations with voltage occur as a result of contamination, ageing, lack of resin cure, delaminated insulation, stress grading systems, and partial discharges, and hence is useful indicator of the insulation health.

Discharge inception voltage: It is the voltage at which partial discharge activity is initiated. The point generally coincides with the point, which the tan d curve with voltage suddenly rises sharply.

Void volume content: Discharges in the insulation could occur in voids or air spaces that may be present in the insulation system if the electric field and air gap size (based on Paschen’s Law) would permit. The volume of discharging voids in the insulation reflects the integrity of the insulation, and is a good indicator of the insulation health. The discharging void volume content can be evaluated from the

variation of the capacitance and tan above discharge inception.

Effective phase of discharging: The effective phase of discharging is estimated from the variation of tan delta and capacitance with voltage above discharge inception. The effective phase is calculated on the basis that all losses and capacitance changes due to partial discharge effects (from internal slot or surface discharging) could effectively occur at an effective phase angle, which is calculated.

Effective phase shift: The effective phase shift is computed from the variation of C-Tan

the variation of capacitance and tan delta with voltage below discharge inception is seen to be linear. The effective phase shift characterizes the stress grading system, and therefore indicates whether properties of stress grading system are modified / deteriorated. Note that when values are greater than 35 deg, the variations are influenced by the conductive properties of the stress grading system or the agent of modification, at the slot exits. Similarly, values lower than 20 deg is indicative of capacitive influences.

Harmonic content: The instantaneous variation of the insulation capacitance with time is plotted from the time waveforms of the voltage and the current data obtained. A harmonic analysis is performed on the instantaneous capacitance-time variation waveform. Harmonic plots are generally seen to be with even harmonic predominance and with reducing magnitudes as the harmonic number increases.

Even to Odd Ratio: This ratio helps us to identify which harmonics (even or odd), are most dominant. Reasons for non-linear behavior of the insulation could either be conductive or charge storage based. Odd harmonic predominance is seen when there are conductive reasons for non-linear behavior, while even harmonic predominance is indicated when the behavior is controlled by charge storage effects.

Check for contamination on the

end-winding at ties/evolutes.


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© Copyright ABB Ltd.

Some of the tests and analysis mentioned in this test report are developed within ABB Ltd. and is property of the same. Unauthorized reproduction of any part of the report, duplication of the report without prior consent of ABB Ltd will be considered illegal.

ABB Limited

Survey No. 110, Behind Kingfisher Factory, Near Nanak Nutrition Factory, Village: Vavanje

MIDC Taloja, Dist.: Raigad, Maharashtra, INDIA

Email: [email protected]

mailto:[email protected]

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